On 10 April 1901, an unusual experiment was conducted in Dorchester, Massachusetts. Dr. Duncan MacDougall was going to prove that the human soul had mass, and was therefore, measurable. He conducted this experiment on six dying patients (selected based upon their imminent death) who were placed on specially made Fairbanks weight scales just prior to their deaths.
In the company of four other doctors, Dr. MacDougall carefully measured the weight of his first patient prior to his death. Once the patient died, an interesting event occurred : “Suddenly, coincident with death,” wrote Macdougall, “the beam end dropped with an audible stroke hitting against the lower limiting bar and remaining there with no rebound. The loss was ascertained to be three-fourths of an ounce.”
The experiment continued on the next patients with the same results. Everything was taken into account and all five doctors took their own measurements and compared their results. Not all the patients lost the same weight, but they did lose something that could not be accounted for.
Following the experiment and consulting with the other attending physicians, it was determined that the average weight loss of each person was ¾ of an ounce. Dr. MacDougall concluded that a human soul weighed 21 grams.
H. LaV. Twining, a physics teacher at Los Angeles Polytechnic High School, attempted the same experiment on mice in 1917. His conclusion was in line with that of Dr. MacDougall.
Later researchers showed that MacDougall’s experimental results were flawed, due to the limitations of the available equipment at the time, a lack of sufficient control over the experimental conditions, and the small sample size. The physicist Robert L. Park raised objections to MacDougall’s findings in his book Superstition: Belief in the Age of Science, while the psychologist Bruce Hood wrote that "Because the weight loss was not reliable or replicable, his findings were unscientific." Dr. Augustus P. Clarke in a rebuttal published in American Medicine pointed that MacDougall failed to consider another obvious hypothesis: that the weight loss (assuming it was real) was due to evaporation caused by the sudden rise in body temperature that occurs when the blood circulation stops and the blood can no longer be air-cooled by the lungs.
Nonetheless, this theory is still popular and a movie titled “21 Grams” made in 2003 references Dr. MacDougall’s experiments. [read more]